Combining neutron diffraction and imaging for residual strain measurements in a single crystal turbine blade

S. Pierret, A. Evans, A.M. Paradowska, A. Kaestner, J. James, T. Etter, H. Van Swygenhoven
NDT & E International, Volume 45, Issue 1, January 2012

Abstract

Neutron diffraction is a technique often used for the non-destructive characterization of residual stresses in engineering materials and components. Measuring stresses within partially hollow objects with complex internal geometry however is challenging due to the difficulties of accurately placing the measurement gage volume in relation to the internal structures. In this study this difficulty is overcome combining surface metrology and neutron tomography to guide the neutron diffraction measurements. Using this technique the triaxial residual strain variations across the airfoil in a single crystal nickel-based superalloy turbine blade have been measured.

Additional Information:

Neutron diffraction is frequently used to investigate non-destructively residual stresses in engineering components. Single crystal (SX) Ni-based superalloy turbine blades usually exhibit complex external geometries with partially internal hollow structures from the cooling channels. Measuring stresses in such a complex component is challenging due to the difficulties of accurately placing the sampling neutron gauge volume in relation to the external geometry and internal features of the blade. In this study, neutron diffraction measurements are guided using a methodology that combines surface metrology and neutron tomography enabling the accurate positioning of the neutron gauge volume to be measured by diffraction. The neutron diffraction measurements revealed large residual strain variations across the airfoil close to the platform in a solution heat-treated SX turbine blade. The residual strain variations are substantially lower when measured further away from the platform.

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